A bearing retainer for a miniature motor

Abstract: A bearing retainer 20 has a hollow body 21 with an open end forming a mouth 25. The mouth opens into an inner void 23 having a bearing support surface 28 for receiving a bearing. The void also has a plurality of axially extending ribs 30 defining a number of lubrication reservoirs or recesses 33. A plurality of teeth 26 extend axially from the open end for engaging a hole in the motor casing to prevent rotation between the retainer and the casing and are deformable to prevent axial separation. Proud coplanar abutment surfaces 27 are respectively disposed between adjacent teeth and bear against the casing to axially align the casing and retainer. The bearing is made by forging, casting or sintering.

Description: This invention relates to a bearing retainer for a miniature motor and to a method of fitting a bearing to a motor casing using the bearing retainer. In particular, the invention relates to a bearing retainer made by forging, casting, sintering or similar molding techniques. The rotor of a fractional horsepower or miniature motor is normally mounted for rotation in bearings supported by an integral end wall of a drawn metal can forming the motor casing and by an end cover or cap closing the casing. The end wall has a hole through which the motor shaft extends. The wall may be deformed to form a recess or housing for the shaft bearing as shown, for example, in GB 2207291. This process is complicated and thus costly to perform with a high degree of accuracy. As an alternative, the bearing may be retained in a bearing retainer which is fitted to the hole in the end wall of the motor casing. The retainer may be a plastic part as shown, for example, in GB 1216146. Here, a plastic ring is used to grip the bearing and retain it with respect to the casing. However, as indicated, the plastic material which makes that method economically viable is not suitable for sleeve or self-aligning sleeve bearings with the motor casing providing the lateral support directly to the bearing. Other bearing retainers of plastics material are disclosed in FR-A-2054015 and JP-A-62081948. The bearing retainer disclosed in FR-A-2054015 is formed according to the preamble of claim 1 and the bearing retainer disclosed in JP-A-62081948 has legs which are passed through holes in the bearing mounting and heat-fusion welded to the mounting. Machined bearing retainers, usually turned parts, formed from aluminium have proved very satisfactory in retaining the bearing axially but there is a problem with the retainer rotating with respect to the casing as the retainer by necessity is round and fitted to a round hole. Also, the cost of providing machined parts is becoming a significant cost component in a miniature motor. Hence, there is a need for an alternative to plastic and machined bearing retainers for the end wall of motor casings for miniature motors. The present invention provides a bearing retainer formed by forging, casting or sintering, which means that the retainer can be produced from steel or other metals giving good dimensional stability and strength and can be formed to mate with non-circular holes in the motor casing, thereby positively preventing rotation of the bearing retainer with respect to the casing. Another advantage of the forging process is that there is no material wastage. Accordingly, one aspect of the present invention provides a method of fitting a bearing to a casing of a miniature electric motor, comprising the steps of drawing the casing into a can-like structure with a closed end and an open end, forming a hole in the closed end of the casing, forming a bearing retainer into a hollow body structure with a central axis and an inner void having a bearing support surface arranged to receive the bearing and with a mouth in one side of the hollow body structure opening the inner void, fitting and securing the retainer to the hole in the closed end of the casing and fitting a bearing to the retainer, wherein the hollow body is formed from metal by forging, casting or sintering, the bearing retainer is formed with a plurality of axially extending teeth formed around the mouth and having abutment surfaces between the teeth, and the retainer is secured to the casing by inserting the teeth through the hole and axially aligning the retainer by abutting the abutment surfaces against the casing and plastically deforming the teeth to axially, radially and rotationally secure the retainer to casing. The provisions of a plurality of teeth which extend into the motor casing allow the hole in the motor casing to be formed with a shape which co-operates with the teeth to positively prevent radial and rotational movement between the retainer and the casing. Preferably, the void has a plurality of ribs defining a plurality of recesses. The radially inner surface of ribs forming at least a part of the bearing support surface. These recesses may form lubrication reservoirs or simply reduce the weight of and the volume of material needed to form the retainer. Preferably, the bearing support surface includes a part-spherical surface portion for receiving a complementary surface of a self-aligning sleeve bearing. Preferably, a depression is formed around the root of each tooth or each abutment surface is bound on opposite sides by depressions. The depressions allow for the non-right angle corner formed between the teeth and the abutment surfaces by the forging process. Also, small burrs which may be formed on the edges of the hole in the casing can be accommodated within the depressions to ensure that the small burrs and/or the rounded corners do not cause axial misalignment between the retainer and the casing. Although the retainer could be formed from aluminium as are the turned retainers or from brass, bronze, etc., a steel retainer, especially one of low carbon steel, may have added advantages. A steel retainer may form part of the return flux path which may be an advantage if a large retainer is used and/or the flux density from the end wall is at or approaching saturation. A steel retainer could form a stronger bond with a steel motor casing by resisting joint failure due to electrolysis erosion and thermal expansion creeping. Preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings. Figure 1 is a sectional side elevation view of a motor casing for a miniature electric motor with a bearing retainer incorporating a bearing. Figure 2 is an outside end view of the casing of Figure 1 shown without the retainer, Figure 3 is an end view of a bearing retainer according to a first embodiment before being fitted to the motor casing; Figure 4 is a sectional side view of the bearing retainer of Figure 3 viewed along section lines IV-IV; Figures 5 and 6 are views similar to Figures 3 and 4 of a bearing retainer according to a second embodiment; and Figure 7 is a perspective view of a bearing retainer according to a further embodiment. A motor casing 10 for a miniature motor is shown in section in Figure 1 fitted with a bearing retainer according to the first embodiment. The casing is a drawn steel can having a tubular side wall 11 with a closed end wall 12 and an open end 13. While the bearing retainer may be formed to accommodate a sleeve bearing, a ball or roller bearing, the preferred embodiments illustrate the bearing retainer being formed with a bearing support surface for a self-aligning sleeve bearing. A self-aligning sleeve bearing or bushing 40 is shown fitted to the retainer 20 and is held in place by a spring (not shown) in the usual manner. A self-aligning bearing is able to swivel slightly within the retainer to accommodate slight misalignment between the retainer/bearing and the shaft. The bearing, however, should not be allowed to freely rotate with respect to the retainer as this would cause wear on the bearing support surface leading to retention and alignment problems. As shown in Figure 2, the end wall 12 has a non-circular aperture 14 for connecting the bearing retainer. The aperture 14 has a castellated margin forming a series of radially inwardly directed projections 15 with intervening spaces 16. The radially outer edge of the spaces 16 and the radially inner edge of the projections 15 form sections of two concentric circles. The bearing retainer 20 is more clearly shown in Figures 3 and 4 and is formed by forging. The retainer is formed with a body portion 21 having a central axis and an inner void 23 for accommodating the bearing. The void opens one end 24 of the body which mates with the housing, to form a mouth 25 with an axially extending teeth 26, which extend into the motor casing through the spaces 16. The projections 15 bear against the mouth 25 of the retainer in between the teeth 26 to axially align the retainer 20 with respect to the casing 10. The portions of the mouth between the teeth 26 form alignment means in the form of abutment surfaces 27 confronting or co-operating with the projections 15. Once in place, the teeth 26 are partially deformed, e.g. by swaging, to secure the retainer in position, thereby preventing axial separation of the retainer and casing. The teeth 26 and the projections 15 intermesh to prevent radial and/or rotational movement of the retainer with respect to the casing, i.e., the radially extending sides of the teeth 26 bear against or contact the radially extending edges of the projections 15. If the inside diameter of the mouth 25, after the teeth have been swaged, is larger than the bearing to be fitted to the bearing retainer, the bearing may be fitted after the retainer has been secured to the casing. However, it is preferred that the bearing be fitted to the retainer before the retainer is secured to the housing as the open end 24 of the retainer 20 faces inwardly of the casing 10. The void has a bearing support surface 28 against which the bearing mates which includes a part-spherical surface 29 to bear against a complementary part-spherical surface of the self-aligning bearing. This part-spherical surface gives the bearing its freedom. The bearing retainer of Figures 5 and 6 is similar with the exception that the void 23 has a number of inwardly extending ribs 30 with the radially inner surface 31 of the ribs forming part of the bearing support surface 28 including the part-spherical surface 29. The part-spherical bearing support surface 29 includes an annular ring formed on the end wall of the retainer with zones extending along the radially inner face of the ribs 30. The ribs also define a number of recesses 33 within the void. The recesses 33 may be used as lubrication reservoirs or left empty. In Figures 5 and 6, the ribs 33 are aligned with the teeth 26 whereas in Figure 7, the ribs 33 are aligned with the abutment surfaces 27. The preferred form for the abutment surfaces 27 is shown more clearly in Figure 7. Each abutment surface has a raised or proud section lying in a common plane between adjacent teeth 26. The proud portion is bounded on opposite sides by depressions 34 formed at the root of the teeth 26. While forging is the preferred method of forming the retainer, other moulding techniques such as casting and sintering may be used to form the retainer. These moulding techniques minimize wastage of material. Forging is preferred because of the speed of production. Cold forging is most preferred to avoid the cost of heating the blanks.

Claims: A method of fitting a bearing to a casing of a miniature electric motor, comprising the steps of: drawing the casing (10) into a can-like structure with a closed end (12) and an open end (13); forming a hole (14) in the closed end (12) of the casing (10); forming a bearing retainer (20) into a hollow body structure (21) with a central axis and an inner void (23) having a bearing support surface (28) arranged to receive the bearing (40) and with a mouth (25) in one side (24) of the hollow body structure (21) opening the inner void (23); fitting and securing the retainer (20) to the hole (14) in the closed end (12) of the casing (10); and fitting a bearing (40) to the retainer (20), characterised in that the hollow body (21) is formed from metal by forging, casting or sintering, the bearing retainer (20) is formed with a plurality of axially extending teeth (26) formed around the mouth (25) and having abutment surfaces (27) between the teeth (26), and the retainer (20) is secured to the casing (10) by inserting the teeth (26) through the hole (14) and axially aligning the retainer (20) by abutting the abutment surfaces (27) against the casing (10) and plastically deforming the teeth (26) to axially, radially and rotationally secure the retainer to casing. A method as defined in Claim 1 wherein the inner void (23) has an inner surface forming a part of the bearing support surface (28), formed with recesses (33) for retaining lubricant for the bearing (40). A method as defined in Claim 2 wherein the inner void (23) is adapted to receive a self-aligning bushing. A method according to any one of the preceding claims further characterised in that the inner void (23) is formed with at least three radially and axially extending ribs (30) on a surface of the inner void forming a plurality of recesses (33) within the inner void (23) and having radially inner faces (31) adapted to receive the bearing (40) and forming part of the bearing support surface (28). A method as defined in any one of the preceding claims wherein a depression (34) is formed around the root of each tooth (26). A method as defined in any one of the preceding claims further characterised in that the bearing retainer (20) is formed by forging a low carbon steel blank. A method as defined in any one of claims 1 to 5 further characterised in that the bearing retainer (20) is formed by sintering. A method according to any one of the preceding claims wherein the hole forming step includes forming a hole (14) of complementary shape to the teeth (26) to form a formlock connection between the retainer (20) and the casing (10) to prevent axial rotation of the retainer (20) with respect to the casing (10); the step of forming the bearing retainer (20) includes forming a plurality of raised abutment surfaces (27) in a common plane between respective adjacent teeth (26) and the fitting step includes abutting the abutment surfaces (27) against the casing (10) while deforming the teeth (26) to axially locate the retainer with respect to the casing. A bearing retainer for fitting a bearing to a casing of a miniature motor, the bearing retainer (20) being in the form of a hollow body (21) having a central axis and comprising: an inner void (23) having a bearing support surface (28) adapted to receive a bearing (40); a mouth (25) formed on one side (24) of the hollow body (21) opening the inner void (23); alignment means for axially aligning the retainer (20) with the casing (10); fixing means for fixing the retainer to a motor casing, axially, radially and rotationally, characterised in that the hollow body (21) is formed from metal by forging, casting or sintering; the fixing means comprises a plurality of plastically deformable teeth (26), extending axially from and circumferentially spaced around the mouth (25); and the alignment means comprises a plurality of abutment surfaces (27) respectively disposed between adjacent teeth (26) and arranged to abut the casing (10). A retainer as defined in Claim 9 characterised in that the inner void (23) has a plurality of ribs (30) defining a plurality of recesses (33), the ribs (30) having radially inner faces (31) forming at least a part of the bearing support surface (28). A retainer as defined in Claim 9 or 10 characterised in that the bearing support surface (28) includes a part-spherical surface portion (29) for receiving a complementary surface of a self-aligning sleeve bearing. A retainer as defined in anyone of Claims 9 to 11 wherein a depression (34) is formed around the root of each tooth (26). A retainer as defined in any one of Claims 9 to 12 wherein the retainer (20) is formed of a low carbon steel. A retainer as defined in any one of Claims 9 to 12 wherein the retainer (20) is a forged bearing retainer. A retainer as defined in any one of Claims 9 to 12 wherein the retainer (20) is a sintered bearing retainer. A retainer as defined in any one of Claims 9 to 12 wherein the retainer (20) is a cast bearing retainer.

Inventors: STROBL GEORG, STROBL, GEORG
Applicants: JOHNSON ELECTRIC SA, JOHNSON ELECTRIC S.A.
Application year: 1994
Main classification: H02K5
IPC codes: F16C23, H02K5, F16C35